cpython/Doc/library/email.message.rst

:mod:`email.message`: Representing an email message
---------------------------------------------------

.. module:: email.message
   :synopsis: The base class representing email messages.
.. moduleauthor:: R. David Murray <rdmurray@bitdance.com>
.. sectionauthor:: R. David Murray <rdmurray@bitdance.com>,
                   Barry A. Warsaw <barry@python.org>

**Source code:** :source:`Lib/email/message.py`

--------------

.. versionadded:: 3.6 [1]_

The central class in the :mod:`email` package is the :class:`EmailMessage`
class, imported from the :mod:`email.message` module.  It is the base class for
the :mod:`email` object model.  :class:`EmailMessage` provides the core
functionality for setting and querying header fields, for accessing message
bodies, and for creating or modifying structured messages.

An email message consists of *headers* and a *payload* (which is also referred
to as the *content*).  Headers are :rfc:`5322` or :rfc:`6532` style field names
and values, where the field name and value are separated by a colon.  The colon
is not part of either the field name or the field value.  The payload may be a
simple text message, or a binary object, or a structured sequence of
sub-messages each with their own set of headers and their own payload.  The
latter type of payload is indicated by the message having a MIME type such as
:mimetype:`multipart/\*` or :mimetype:`message/rfc822`.

The conceptual model provided by an :class:`EmailMessage` object is that of an
ordered dictionary of headers coupled with a *payload* that represents the
:rfc:`5322` body of the message, which might be a list of sub-``EmailMessage``
objects.  In addition to the normal dictionary methods for accessing the header
names and values, there are methods for accessing specialized information from
the headers (for example the MIME content type), for operating on the payload,
for generating a serialized version of the message, and for recursively walking
over the object tree.

The :class:`EmailMessage` dictionary-like interface is indexed by the header
names, which must be ASCII values.  The values of the dictionary are strings
with some extra methods.  Headers are stored and returned in case-preserving
form, but field names are matched case-insensitively.  The keys are ordered,
but unlike a real dict, there can be duplicates.  Addtional methods are
provided for working with headers that have duplicate keys.

The *payload* is either a string or bytes object, in the case of simple message
objects, or a list of :class:`EmailMessage` objects, for MIME container
documents such as :mimetype:`multipart/\*` and :mimetype:`message/rfc822`
message objects.


.. class:: EmailMessage(policy=default)

   If *policy* is specified use the rules it specifies to update and serialize
   the representation of the message.  If *policy* is not set, use the
   :class:`~email.policy.default` policy, which follows the rules of the email
   RFCs except for line endings (instead of the RFC mandated ``\r\n``, it uses
   the Python standard ``\n`` line endings).  For more information see the
   :mod:`~email.policy` documentation.

   .. method:: as_string(unixfrom=False, maxheaderlen=None, policy=None)

      Return the entire message flattened as a string.  When optional
      *unixfrom* is true, the envelope header is included in the returned
      string.  *unixfrom* defaults to ``False``.  For backward compatibility
      with the base :class:`~email.message.Message` class *maxheaderlen* is
      accepted, but defaults to ``None``, which means that by default the line
      length is controlled by the
      :attr:`~email.policy.Policy.max_line_length` of the policy.  The
      *policy* argument may be used to override the default policy obtained
      from the message instance.  This can be used to control some of the
      formatting produced by the method, since the specified *policy* will be
      passed to the :class:`~email.generator.Generator`.

      Flattening the message may trigger changes to the :class:`EmailMessage`
      if defaults need to be filled in to complete the transformation to a
      string (for example, MIME boundaries may be generated or modified).

      Note that this method is provided as a convenience and may not be the
      most useful way to serialize messages in your application, especially if
      you are dealing with multiple messages.  See
      :class:`email.generator.Generator` for a more flexible API for
      serializing messages.  Note also that this method is restricted to
      producing messages serialized as "7 bit clean" when
      :attr:`~email.policy.EmailPolicy.utf8` is ``False``, which is the default.

      .. versionchanged:: 3.6 the default behavior when *maxheaderlen*
         is not specified was changed from defaulting to 0 to defaulting
         to the value of *max_line_length* from the policy.


   .. method:: __str__()

      Equivalent to ``as_string(policy=self.policy.clone(utf8=True))``.  Allows
      ``str(msg)`` to produce a string containing the serialized message in a
      readable format.

      .. versionchanged:: 3.4 the method was changed to use ``utf8=True``,
         thus producing an :rfc:`6531`-like message representation, instead of
         being a direct alias for :meth:`as_string`.


   .. method:: as_bytes(unixfrom=False, policy=None)

      Return the entire message flattened as a bytes object.  When optional
      *unixfrom* is true, the envelope header is included in the returned
      string.  *unixfrom* defaults to ``False``.  The *policy* argument may be
      used to override the default policy obtained from the message instance.
      This can be used to control some of the formatting produced by the
      method, since the specified *policy* will be passed to the
      :class:`~email.generator.BytesGenerator`.

      Flattening the message may trigger changes to the :class:`EmailMessage`
      if defaults need to be filled in to complete the transformation to a
      string (for example, MIME boundaries may be generated or modified).

      Note that this method is provided as a convenience and may not be the
      most useful way to serialize messages in your application, especially if
      you are dealing with multiple messages.  See
      :class:`email.generator.BytesGenerator` for a more flexible API for
      serializing messages.


   .. method:: __bytes__()

      Equivalent to :meth:`.as_bytes()`.  Allows ``bytes(msg)`` to produce a
      bytes object containing the serialized message.


   .. method:: is_multipart()

      Return ``True`` if the message's payload is a list of
      sub-\ :class:`EmailMessage` objects, otherwise return ``False``.  When
      :meth:`is_multipart` returns ``False``, the payload should be a string
      object (which might be a CTE encoded binary payload).  Note that
      :meth:`is_multipart` returning ``True`` does not necessarily mean that
      "msg.get_content_maintype() == 'multipart'" will return the ``True``.
      For example, ``is_multipart`` will return ``True`` when the
      :class:`EmailMessage` is of type ``message/rfc822``.


   .. method:: set_unixfrom(unixfrom)

      Set the message's envelope header to *unixfrom*, which should be a
      string.  (See :class:`~mailbox.mboxMessage` for a brief description of
      this header.)


   .. method:: get_unixfrom()

      Return the message's envelope header.  Defaults to ``None`` if the
      envelope header was never set.


   The following methods implement the mapping-like interface for accessing the
   message's headers.  Note that there are some semantic differences
   between these methods and a normal mapping (i.e. dictionary) interface.  For
   example, in a dictionary there are no duplicate keys, but here there may be
   duplicate message headers.  Also, in dictionaries there is no guaranteed
   order to the keys returned by :meth:`keys`, but in an :class:`EmailMessage`
   object, headers are always returned in the order they appeared in the
   original message, or in which they were added to the message later.  Any
   header deleted and then re-added is always appended to the end of the
   header list.

   These semantic differences are intentional and are biased toward
   convenience in the most common use cases.

   Note that in all cases, any envelope header present in the message is not
   included in the mapping interface.


   .. method:: __len__()

      Return the total number of headers, including duplicates.


   .. method:: __contains__(name)

      Return ``True`` if the message object has a field named *name*. Matching is
      done without regard to case and *name* does not include the trailing
      colon.  Used for the ``in`` operator.  For example::

           if 'message-id' in myMessage:
              print('Message-ID:', myMessage['message-id'])


   .. method:: __getitem__(name)

      Return the value of the named header field.  *name* does not include the
      colon field separator.  If the header is missing, ``None`` is returned; a
      :exc:`KeyError` is never raised.

      Note that if the named field appears more than once in the message's
      headers, exactly which of those field values will be returned is
      undefined.  Use the :meth:`get_all` method to get the values of all the
      extant headers named *name*.

      Using the standard (non-``compat32``) policies, the returned value is an
      instance of a subclass of :class:`email.headerregistry.BaseHeader`.


   .. method:: __setitem__(name, val)

      Add a header to the message with field name *name* and value *val*.  The
      field is appended to the end of the message's existing headers.

      Note that this does *not* overwrite or delete any existing header with the same
      name.  If you want to ensure that the new header is the only one present in the
      message with field name *name*, delete the field first, e.g.::

         del msg['subject']
         msg['subject'] = 'Python roolz!'

      If the :mod:`policy <email.policy>` defines certain headers to be unique (as the standard
      policies do), this method may raise a :exc:`ValueError` when an attempt
      is made to assign a value to such a header when one already exists.  This
      behavior is intentional for consistency's sake, but do not depend on it
      as we may choose to make such assignments do an automatic deletion of the
      existing header in the future.


   .. method:: __delitem__(name)

      Delete all occurrences of the field with name *name* from the message's
      headers.  No exception is raised if the named field isn't present in the
      headers.


   .. method:: keys()

      Return a list of all the message's header field names.


   .. method:: values()

      Return a list of all the message's field values.


   .. method:: items()

      Return a list of 2-tuples containing all the message's field headers and
      values.


   .. method:: get(name, failobj=None)

      Return the value of the named header field.  This is identical to
      :meth:`~object.__getitem__` except that optional *failobj* is returned if the
      named header is missing (*failobj* defaults to ``None``).


   Here are some additional useful header related methods:


   .. method:: get_all(name, failobj=None)

      Return a list of all the values for the field named *name*. If there are
      no such named headers in the message, *failobj* is returned (defaults to
      ``None``).


   .. method:: add_header(_name, _value, **_params)

      Extended header setting.  This method is similar to :meth:`__setitem__`
      except that additional header parameters can be provided as keyword
      arguments.  *_name* is the header field to add and *_value* is the
      *primary* value for the header.

      For each item in the keyword argument dictionary *_params*, the key is
      taken as the parameter name, with underscores converted to dashes (since
      dashes are illegal in Python identifiers).  Normally, the parameter will
      be added as ``key="value"`` unless the value is ``None``, in which case
      only the key will be added.

      If the value contains non-ASCII characters, the charset and language may
      be explicitly controlled by specifying the value as a three tuple in the
      format ``(CHARSET, LANGUAGE, VALUE)``, where ``CHARSET`` is a string
      naming the charset to be used to encode the value, ``LANGUAGE`` can
      usually be set to ``None`` or the empty string (see :rfc:`2231` for other
      possibilities), and ``VALUE`` is the string value containing non-ASCII
      code points.  If a three tuple is not passed and the value contains
      non-ASCII characters, it is automatically encoded in :rfc:`2231` format
      using a ``CHARSET`` of ``utf-8`` and a ``LANGUAGE`` of ``None``.

      Here is an example::

         msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')

      This will add a header that looks like ::

         Content-Disposition: attachment; filename="bud.gif"

      An example of the extended interface with non-ASCII characters::

         msg.add_header('Content-Disposition', 'attachment',
                        filename=('iso-8859-1', '', 'Fußballer.ppt'))


   .. method:: replace_header(_name, _value)

      Replace a header.  Replace the first header found in the message that
      matches *_name*, retaining header order and field name case of the
      original header.  If no matching header is found, raise a
      :exc:`KeyError`.


   .. method:: get_content_type()

      Return the message's content type, coerced to lower case of the form
      :mimetype:`maintype/subtype`.  If there is no :mailheader:`Content-Type`
      header in the message return the value returned by
      :meth:`get_default_type`.  If the :mailheader:`Content-Type` header is
      invalid, return ``text/plain``.

      (According to :rfc:`2045`, messages always have a default type,
      :meth:`get_content_type` will always return a value.  :rfc:`2045` defines
      a message's default type to be :mimetype:`text/plain` unless it appears
      inside a :mimetype:`multipart/digest` container, in which case it would
      be :mimetype:`message/rfc822`.  If the :mailheader:`Content-Type` header
      has an invalid type specification, :rfc:`2045` mandates that the default
      type be :mimetype:`text/plain`.)


   .. method:: get_content_maintype()

      Return the message's main content type.  This is the :mimetype:`maintype`
      part of the string returned by :meth:`get_content_type`.


   .. method:: get_content_subtype()

      Return the message's sub-content type.  This is the :mimetype:`subtype`
      part of the string returned by :meth:`get_content_type`.


   .. method:: get_default_type()

      Return the default content type.  Most messages have a default content
      type of :mimetype:`text/plain`, except for messages that are subparts of
      :mimetype:`multipart/digest` containers.  Such subparts have a default
      content type of :mimetype:`message/rfc822`.


   .. method:: set_default_type(ctype)

      Set the default content type.  *ctype* should either be
      :mimetype:`text/plain` or :mimetype:`message/rfc822`, although this is
      not enforced.  The default content type is not stored in the
      :mailheader:`Content-Type` header, so it only affects the return value of
      the ``get_content_type`` methods when no :mailheader:`Content-Type`
      header is present in the message.


   .. method:: set_param(param, value, header='Content-Type', requote=True, \
                         charset=None, language='', replace=False)

      Set a parameter in the :mailheader:`Content-Type` header.  If the
      parameter already exists in the header, replace its value with *value*.
      When *header* is ``Content-Type`` (the default) and the header does not
      yet exist in the message, add it, set its value to
      :mimetype:`text/plain`, and append the new parameter value.  Optional
      *header* specifies an alternative header to :mailheader:`Content-Type`.

      If the value contains non-ASCII characters, the charset and language may
      be explicitly specified using the optional *charset* and *language*
      parameters.  Optional *language* specifies the :rfc:`2231` language,
      defaulting to the empty string.  Both *charset* and *language* should be
      strings.  The default is to use the ``utf8`` *charset* and ``None`` for
      the *language*.

      If *replace* is ``False`` (the default) the header is moved to the
      end of the list of headers.  If *replace* is ``True``, the header
      will be updated in place.

      Use of the *requote* parameter with :class:`EmailMessage` objects is
      deprecated.

      Note that existing parameter values of headers may be accessed through
      the :attr:`~email.headerregistry.ParameterizedMIMEHeader.params` attribute of the
      header value (for example, ``msg['Content-Type'].params['charset']``).

      .. versionchanged:: 3.4 ``replace`` keyword was added.


   .. method:: del_param(param, header='content-type', requote=True)

      Remove the given parameter completely from the :mailheader:`Content-Type`
      header.  The header will be re-written in place without the parameter or
      its value.  Optional *header* specifies an alternative to
      :mailheader:`Content-Type`.

      Use of the *requote* parameter with :class:`EmailMessage` objects is
      deprecated.


   .. method:: get_filename(failobj=None)

      Return the value of the ``filename`` parameter of the
      :mailheader:`Content-Disposition` header of the message.  If the header
      does not have a ``filename`` parameter, this method falls back to looking
      for the ``name`` parameter on the :mailheader:`Content-Type` header.  If
      neither is found, or the header is missing, then *failobj* is returned.
      The returned string will always be unquoted as per
      :func:`email.utils.unquote`.


   .. method:: get_boundary(failobj=None)

      Return the value of the ``boundary`` parameter of the
      :mailheader:`Content-Type` header of the message, or *failobj* if either
      the header is missing, or has no ``boundary`` parameter.  The returned
      string will always be unquoted as per :func:`email.utils.unquote`.


   .. method:: set_boundary(boundary)

      Set the ``boundary`` parameter of the :mailheader:`Content-Type` header to
      *boundary*.  :meth:`set_boundary` will always quote *boundary* if
      necessary.  A :exc:`~email.errors.HeaderParseError` is raised if the
      message object has no :mailheader:`Content-Type` header.

      Note that using this method is subtly different from deleting the old
      :mailheader:`Content-Type` header and adding a new one with the new
      boundary via :meth:`add_header`, because :meth:`set_boundary` preserves
      the order of the :mailheader:`Content-Type` header in the list of
      headers.


   .. method:: get_content_charset(failobj=None)

      Return the ``charset`` parameter of the :mailheader:`Content-Type` header,
      coerced to lower case.  If there is no :mailheader:`Content-Type` header, or if
      that header has no ``charset`` parameter, *failobj* is returned.


   .. method:: get_charsets(failobj=None)

      Return a list containing the character set names in the message.  If the
      message is a :mimetype:`multipart`, then the list will contain one element
      for each subpart in the payload, otherwise, it will be a list of length 1.

      Each item in the list will be a string which is the value of the
      ``charset`` parameter in the :mailheader:`Content-Type` header for the
      represented subpart.  If the subpart has no :mailheader:`Content-Type`
      header, no ``charset`` parameter, or is not of the :mimetype:`text` main
      MIME type, then that item in the returned list will be *failobj*.


   .. method:: is_attachment

      Return ``True`` if there is a :mailheader:`Content-Disposition` header
      and its (case insensitive) value is ``attachment``, ``False`` otherwise.

      .. versionchanged:: 3.4.2
         is_attachment is now a method instead of a property, for consistency
         with :meth:`~email.message.Message.is_multipart`.


   .. method:: get_content_disposition()

      Return the lowercased value (without parameters) of the message's
      :mailheader:`Content-Disposition` header if it has one, or ``None``.  The
      possible values for this method are *inline*, *attachment* or ``None``
      if the message follows :rfc:`2183`.

      .. versionadded:: 3.5


   The following methods relate to interrogating and manipulating the content
   (payload) of the message.


   .. method:: walk()

      The :meth:`walk` method is an all-purpose generator which can be used to
      iterate over all the parts and subparts of a message object tree, in
      depth-first traversal order.  You will typically use :meth:`walk` as the
      iterator in a ``for`` loop; each iteration returns the next subpart.

      Here's an example that prints the MIME type of every part of a multipart
      message structure:

      .. testsetup::

         from email import message_from_binary_file
         with open('../Lib/test/test_email/data/msg_16.txt', 'rb') as f:
             msg = message_from_binary_file(f)

      .. doctest::

         >>> for part in msg.walk():
         ...     print(part.get_content_type())
         multipart/report
         text/plain
         message/delivery-status
         text/plain
         text/plain
         message/rfc822
         text/plain

      ``walk`` iterates over the subparts of any part where
      :meth:`is_multipart` returns ``True``, even though
      ``msg.get_content_maintype() == 'multipart'`` may return ``False``.  We
      can see this in our example by making use of the ``_structure`` debug
      helper function:

      .. doctest::

         >>> from email.iterators import _structure
         >>> for part in msg.walk():
         ...     print(part.get_content_maintype() == 'multipart',
         ...           part.is_multipart())
         True True
         False False
         False True
         False False
         False False
         False True
         False False
         >>> _structure(msg)
         multipart/report
             text/plain
             message/delivery-status
                 text/plain
                 text/plain
             message/rfc822
                 text/plain

      Here the ``message`` parts are not ``multiparts``, but they do contain
      subparts. ``is_multipart()`` returns ``True`` and ``walk`` descends
      into the subparts.


   .. method:: get_body(preferencelist=('related', 'html', 'plain'))

      Return the MIME part that is the best candidate to be the "body" of the
      message.

      *preferencelist* must be a sequence of strings from the set ``related``,
      ``html``, and ``plain``, and indicates the order of preference for the
      content type of the part returned.

      Start looking for candidate matches with the object on which the
      ``get_body`` method is called.

      If ``related`` is not included in *preferencelist*, consider the root
      part (or subpart of the root part) of any related encountered as a
      candidate if the (sub-)part matches a preference.

      When encountering a ``multipart/related``, check the ``start`` parameter
      and if a part with a matching :mailheader:`Content-ID` is found, consider
      only it when looking for candidate matches.  Otherwise consider only the
      first (default root) part of the ``multipart/related``.

      If a part has a :mailheader:`Content-Disposition` header, only consider
      the part a candidate match if the value of the header is ``inline``.

      If none of the candidates matches any of the preferences in
      *preferencelist*, return ``None``.

      Notes: (1) For most applications the only *preferencelist* combinations
      that really make sense are ``('plain',)``, ``('html', 'plain')``, and the
      default ``('related', 'html', 'plain')``.  (2) Because matching starts
      with the object on which ``get_body`` is called, calling ``get_body`` on
      a ``multipart/related`` will return the object itself unless
      *preferencelist* has a non-default value. (3) Messages (or message parts)
      that do not specify a :mailheader:`Content-Type` or whose
      :mailheader:`Content-Type` header is invalid will be treated as if they
      are of type ``text/plain``, which may occasionally cause ``get_body`` to
      return unexpected results.


   .. method:: iter_attachments()

      Return an iterator over all of the immediate sub-parts of the message
      that are not candidate "body" parts.  That is, skip the first occurrence
      of each of ``text/plain``, ``text/html``, ``multipart/related``, or
      ``multipart/alternative`` (unless they are explicitly marked as
      attachments via :mailheader:`Content-Disposition: attachment`), and
      return all remaining parts.  When applied directly to a
      ``multipart/related``, return an iterator over the all the related parts
      except the root part (ie: the part pointed to by the ``start`` parameter,
      or the first part if there is no ``start`` parameter or the ``start``
      parameter doesn't match the :mailheader:`Content-ID` of any of the
      parts).  When applied directly to a ``multipart/alternative`` or a
      non-``multipart``, return an empty iterator.


   .. method:: iter_parts()

      Return an iterator over all of the immediate sub-parts of the message,
      which will be empty for a non-``multipart``.  (See also
      :meth:`~email.message.EmailMessage.walk`.)


   .. method:: get_content(*args, content_manager=None, **kw)

      Call the :meth:`~email.contentmanager.ContentManager.get_content` method
      of the *content_manager*, passing self as the message object, and passing
      along any other arguments or keywords as additional arguments.  If
      *content_manager* is not specified, use the ``content_manager`` specified
      by the current :mod:`~email.policy`.


   .. method:: set_content(*args, content_manager=None, **kw)

      Call the :meth:`~email.contentmanager.ContentManager.set_content` method
      of the *content_manager*, passing self as the message object, and passing
      along any other arguments or keywords as additional arguments.  If
      *content_manager* is not specified, use the ``content_manager`` specified
      by the current :mod:`~email.policy`.


   .. method:: make_related(boundary=None)

      Convert a non-``multipart`` message into a ``multipart/related`` message,
      moving any existing :mailheader:`Content-` headers and payload into a
      (new) first part of the ``multipart``.  If *boundary* is specified, use
      it as the boundary string in the multipart, otherwise leave the boundary
      to be automatically created when it is needed (for example, when the
      message is serialized).


   .. method:: make_alternative(boundary=None)

      Convert a non-``multipart`` or a ``multipart/related`` into a
      ``multipart/alternative``, moving any existing :mailheader:`Content-`
      headers and payload into a (new) first part of the ``multipart``.  If
      *boundary* is specified, use it as the boundary string in the multipart,
      otherwise leave the boundary to be automatically created when it is
      needed (for example, when the message is serialized).


   .. method:: make_mixed(boundary=None)

      Convert a non-``multipart``, a ``multipart/related``, or a
      ``multipart-alternative`` into a ``multipart/mixed``, moving any existing
      :mailheader:`Content-` headers and payload into a (new) first part of the
      ``multipart``.  If *boundary* is specified, use it as the boundary string
      in the multipart, otherwise leave the boundary to be automatically
      created when it is needed (for example, when the message is serialized).


   .. method:: add_related(*args, content_manager=None, **kw)

      If the message is a ``multipart/related``, create a new message
      object, pass all of the arguments to its :meth:`set_content` method,
      and :meth:`~email.message.Message.attach` it to the ``multipart``.  If
      the message is a non-``multipart``, call :meth:`make_related` and then
      proceed as above.  If the message is any other type of ``multipart``,
      raise a :exc:`TypeError`. If *content_manager* is not specified, use
      the ``content_manager`` specified by the current :mod:`~email.policy`.
      If the added part has no :mailheader:`Content-Disposition` header,
      add one with the value ``inline``.


   .. method:: add_alternative(*args, content_manager=None, **kw)

      If the message is a ``multipart/alternative``, create a new message
      object, pass all of the arguments to its :meth:`set_content` method, and
      :meth:`~email.message.Message.attach` it to the ``multipart``.  If the
      message is a non-``multipart`` or ``multipart/related``, call
      :meth:`make_alternative` and then proceed as above.  If the message is
      any other type of ``multipart``, raise a :exc:`TypeError`. If
      *content_manager* is not specified, use the ``content_manager`` specified
      by the current :mod:`~email.policy`.


   .. method:: add_attachment(*args, content_manager=None, **kw)

      If the message is a ``multipart/mixed``, create a new message object,
      pass all of the arguments to its :meth:`set_content` method, and
      :meth:`~email.message.Message.attach` it to the ``multipart``.  If the
      message is a non-``multipart``, ``multipart/related``, or
      ``multipart/alternative``, call :meth:`make_mixed` and then proceed as
      above. If *content_manager* is not specified, use the ``content_manager``
      specified by the current :mod:`~email.policy`.  If the added part
      has no :mailheader:`Content-Disposition` header, add one with the value
      ``attachment``.  This method can be used both for explicit attachments
      (:mailheader:`Content-Disposition: attachment`) and ``inline`` attachments
      (:mailheader:`Content-Disposition: inline`), by passing appropriate
      options to the ``content_manager``.


   .. method:: clear()

      Remove the payload and all of the headers.


   .. method:: clear_content()

      Remove the payload and all of the :mailheader:`!Content-` headers, leaving
      all other headers intact and in their original order.


   :class:`EmailMessage` objects have the following instance attributes:


   .. attribute:: preamble

      The format of a MIME document allows for some text between the blank line
      following the headers, and the first multipart boundary string. Normally,
      this text is never visible in a MIME-aware mail reader because it falls
      outside the standard MIME armor.  However, when viewing the raw text of
      the message, or when viewing the message in a non-MIME aware reader, this
      text can become visible.

      The *preamble* attribute contains this leading extra-armor text for MIME
      documents.  When the :class:`~email.parser.Parser` discovers some text
      after the headers but before the first boundary string, it assigns this
      text to the message's *preamble* attribute.  When the
      :class:`~email.generator.Generator` is writing out the plain text
      representation of a MIME message, and it finds the
      message has a *preamble* attribute, it will write this text in the area
      between the headers and the first boundary.  See :mod:`email.parser` and
      :mod:`email.generator` for details.

      Note that if the message object has no preamble, the *preamble* attribute
      will be ``None``.


   .. attribute:: epilogue

      The *epilogue* attribute acts the same way as the *preamble* attribute,
      except that it contains text that appears between the last boundary and
      the end of the message.  As with the :attr:`~EmailMessage.preamble`,
      if there is no epilog text this attribute will be ``None``.


   .. attribute:: defects

      The *defects* attribute contains a list of all the problems found when
      parsing this message.  See :mod:`email.errors` for a detailed description
      of the possible parsing defects.


.. class:: MIMEPart(policy=default)

    This class represents a subpart of a MIME message.  It is identical to
    :class:`EmailMessage`, except that no :mailheader:`MIME-Version` headers are
    added when :meth:`~EmailMessage.set_content` is called, since sub-parts do
    not need their own :mailheader:`MIME-Version` headers.


.. rubric:: Footnotes

.. [1] Originally added in 3.4 as a :term:`provisional module <provisional
       package>`.  Docs for legacy message class moved to
       :ref:`compat32_message`.